Windows Live Messenger and Yahoo! Messenger with Voice users in the U.S. and more than 15 international markets can register to participatein the IM interoperability beta by visiting Yahoo!.The new beta program will be available in Argentina, Australia, Brazil,Canada (English and French), China, France, Germany, Hong Kong, India,Italy, Korea, Mexico, Netherlands, Singapore, Spain, Taiwan, Turkey,the United Kingdom and the United States (English and Spanish).

Personally I am not a fan of Microsoft nor Yahoo Messenger. The solution is Jabber! OpenSource and free! There are alot of Transports which give the user the possibility to connect to other Messenger Networks.